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Explaining Cold Water Accumulators

What is a Cold Water Accumulator?

Cold water accumulators are an efficient, energy saving way to deal with the problem of low incoming water pressure to your heating system, and the simplest way to think of them is as a large water storage tank which adds water, topping up the heating system when the demand is greatest.

They consist of a steel tank with two chambers separated by a diaphragm. One side of the diaphragm is sealed and pressurized with compressed air; the other side is open to the water system.

When you open an outlet such as a bathroom tap, water initially flows from the accumulator until the pressure drops enough for the pump to turn on. As the pump runs it provides the water flow required by the open outlet. When the outlet is switched off the pump will continue to run until the cold water accumulator has re-pressurized itself to the pressure that the setting on the pump will shut off at.

How much will a Cold Water Accumulator increase my water pressure by?

A common misconception. Accumulators do not increase water pressure. They simply allow the system to work at its maximum pressure capability. Each hot water system has a standing pressure and a working pressure. Just as it sounds, standing pressure is the pressure that exists when no outlets are being used and the water is at rest. This pressure will drop to working pressure when taps or showers are being used.

A cold water accumulator works by supplementing the flow of water when the system has open outlets, thus raising the flow back up to standing pressure even though outlets are open and it would normally be under working pressure. When the outlets are closed, the accumulator shuts off the additional flow until it is needed again.

Can I use a Cold Water Accumulator with my existing Combi Boiler?

Yes. Combination boilers with a poor rate of flow can be used in conjunction with a cold water accumulator, allowing the boiler to run at its max rate of flow and not be interrupted if a second outlet is switched on during a shower.

Where can I install a Cold Water Accumulator?

Accumulators come in many different sizes and styles. Specially designed models are suitable for exterior installation such as in an open garage or shed. There are no drainage requirements and no power supply is needed for an accumulator so the only concern is the pipe work that will need to run from the accumulator to the house. Depending on the size and shape of a cold water accumulator it may or may not be suitable for horizontal installation, say in a loft. Make sure you are buying the correct model for your needs.

What are the regulations regarding Cold Water Accumulators?

A cold water accumulator can be installed anywhere on the mains supply entering the property and there must be a check valve installed on the main supply. A 3.5 bar pressure reducing valve will also have to be fitted if the pressure is likely to rise above 5 bar.

The air pressure inside an accumulator is set at 2 bar but may need adjusting so that it is between 1 1.5 bar below the mains pressure. The minimum this can be set to is 0.5 bar but this will require consulting the manufacturer.

The lower the mains pressure is, the less water that may be stored in the accumulator, so always remember to oversize the accumulator by at least one clear size more than your unvented cylinder or flow rate requirements.

I have a shared water main. Can I still install a Cold Water Accumulator?

Yes. Cold water accumulators can be installed on 15mm (small bore) or even on shared main supplies as long as you carry out pressure and flow tests and oversize the accumulator to not only meet but exceed the expected demand.

Is there anything else I should know about Cold Water Accumulators?

A correctly sized accumulator will allow almost any number of baths or showers to be taken at the same time, regardless of the incoming main flow rate, and will keep working even if the mains are turned off, irrespective of the mains water pressure

Requiring no power supply, generating no noise, consuming no energy and needing no ongoing maintenance, a cold water accumulator is the most economical and environmentally friendly possible option for households suffering from low mains pressure.